Here's what we know -- Nevada H.S. was facing off against Carlisle H.S. in Iowa on Tuesday ... and when both teams lined up to say "good game" after Nevada's 72-47 win, #4 on Carlisle attacked #5 on Nevada.

Unclear what happened in the game, but it appears the players were going through the line without incident before the Carlisle guard threw punches to the opponent's stomach and head.

The player who was attacked then falls to the ground as other players and coaches step in to put a stop to the altercation ... with the Carlisle player getting wrestled to the ground.

We spoke with Nevada superintendent Dr. Steve Gray, who tells us the player is currently doing okay.

"It's a very unfortunate situation," he tells TMZ Sports. "I'm happy they deescalated it. I thought our coaches and staff handled it well and got everyone out of there without it worsening."

Carlisle PD tells us they are aware of the incident and an investigation is underway.

An officer was present during the game, but the player was not arrested.

The Carlisle superintendent tells us ... "This is without question an unfortunate incident that is not representative of the school culture that exists in Carlisle Community School District."

"I want to make it clear that this type of conduct is not tolerated at Carlisle CSD. The district will follow the student code of conduct policy and procedures throughout the investigation of this incident and implement appropriate consequences.

"All proper authorities have been notified of the incident including IHSAA."